The objective of our work is to get a detailed knowledge of the molecular events of the assembly of the head of bacteriophage T4. Within the context of this proposal, we will study the protein-protein interaction related to the assembly of the head, we will study the initiation of the DNA packaging process and try to elucidate the actual DNA-packaging mechanism. We will study the genes and proteins involved in the actual DNA-packaging process and characterize the proteolytic activity associated with the maturation of the head. Attempts will be made to convert the various intermediate head structures to the mature head in vitro.